Some company just teamed up with Rustoleum to create a product called Never Wet. After watching some videos, I'm convinced this stuff is awesome. They sprayed an iphone with it and submerged it, so It looks like it could be clear enough to go on sunglasses. $20 a can at Lowes or homedepot but you need 2 cans, one base coat and top coat. $40 is a lot but im sure you could find excellent uses for two big cans.